- "How unsorrowed I will be to see you, my friends. One day soon. On the longer path."
- ―Sy-O's thoughts on its departed visitors
Sy-O was a young exogorth that lived a solitary life in an asteroid within the Hoth asteroid belt. Sy-O attempted to capture the Millennium Falcon and its crew in order to make them a part of their internal ecosystem and meet the social standards of its kind by having a more diverse ecosystem.
- Star Wars: Episode V The Empire Strikes Back (First appearance)
- Star Wars Galaxy of Adventures – "Han Solo vs. the Space Slug - The Escape Artist"
- The Empire Strikes Back: So You Want to Be a Jedi?
- Star Wars: The Empire Strikes Back junior novelization
- Star Wars: The Empire Strikes Back Screen Comix
- "An Unusual Hiding Place"—The Original Trilogy Stories
- "Amara Kel's Rules for TIE Pilot Survival (Probably)"—From a Certain Point of View: The Empire Strikes Back
- "This Is No Cave"—From a Certain Point of View: The Empire Strikes Back (First identified as Sy-O)
- "Lord Vader Will See You Now"—From a Certain Point of View: The Empire Strikes Back (Mentioned only)
- Star Wars Helmet Collection 6 (Highlights of the Saga: Peril in the Asteroid Field) (Indirect mention only)
- Star Wars Helmet Collection 51 (Databank A-Z: Soulless One–Super Battle Droids)
- Star Wars Helmet Collection 61 (Highlights of the Saga: Escaping Cloud City) (Indirect mention only)
- Star Wars Day-at-a-Time Calendar 2020
- "Battle of Hoth and the Second Death Star" – Star Wars Encyclopedia (Picture only)